As a unit for evaluating an influence of radio waves transmitted from a radio device such as a mobile phone, an SAR (Specific Absorption Rate) is used. The SAR indicates the amount of energy absorbed in a unit of time with respect to a tissue per unit mass of a human body exposed to radio waves. In Japan, based on a guideline indicated by WHO (World Health Organization), “a local SAR fails to exceed an allowed value of 2 W/kg” with regard to portable devices is obliged by an Ordinance of the Ministry of Internal Affairs and Communications.
Therefore, some portable information processing devices such as a mobile phone and a notebook PC (Personal Computer) stop an output of radio waves from an antenna, or reduce its output when detecting that their own devices each come close to a human body. For example, based on detection results of a display direction of a screen, when detecting that antennas come close to users, some tablet PCs stop an output of radio waves from the antennas. Some tablet PCs further detect a display direction of a screen by using a tilt sensor.
Japanese Laid-open Patent Publication No. 2008-90345
Japanese Laid-open Patent Publication No. 2009-152705
Incidentally, nations slightly differ from each other in interpretations of a standard of SAR. For example, as an object for restricting the SAR, there are some nations in which knees or thighs are included, and the other nations in which they are not included. In the case where knees or thighs are included as an object for restricting the SAR, for example, when an information processing device is mounted and used on knees in the seated state, radiated waves to a vertically downward direction of the information processing device need to be restricted.
In a notebook PC on which an antenna is mounted near a chassis of a display unit, even when it is mounted and used on user's knees, the antenna may be sufficiently separated from the user's knees or thighs so as to satisfy a standard of the SAR. Suppose further that a so-called convertible PC is mounted on user's knees, which is used as both of a notebook PC mode and a tablet PC mode. Even in this case, when a PC main body or display unit has a certain degree of thickness, an antenna in the tablet PC mode may be separated from the user's knees or thighs.
However, since thinning of a convertible PC advances recently, an antenna fails to be sufficiently separated from user's knees or thighs, and as a result a standard of the SAR is not satisfied. In this respect, much the same is true on a slate information processing device. Although not limited to the above devices, the thinning is demanded in various information processing devices. In a thinned information processing device, even if mounted in an internal portion or on a top side of the device, an antenna fails to be sufficiently separated from user's knees or thighs located in a vertically downward side.